1. Dep. of Geoscience; Univ. of Nevada Las Vegas; 4505 S. Maryland Parkway Las Vegas NV 89154-4010
2. Geography Research Group KU Leuven Dep. of Earth and Environ. Sci.; Geo-Institute; Celestijnenlaan 200E 3001 Leuven Belgium
3. W.M. Keck Science Dep.; Claremont McKenna, Pitzer, and Scripps Colleges; 925 N. Mills Avenue Claremont CA 91711
4. U.S. Geological Survey-Geosciences and Environ. Change Sci. Center; Box 25046 MS-980 Denver CO 80225